Earth, Moon, and SunBy: A. Taylor

Key Concepts

Section 1 - Earth in SpaceHowdoesEarthmoveinspace?

Earth moves through space by rotation and revolution. Rotation is the motion of Earth spinning on its axis, also causing day and night. Revolution is the movement of Earth on its orbit circling around the sun. Calendars are based off how long it takes for Earth to cycle in its orbit, about 365.25 days.

What causes the seasons on Earth?

The cycle of seasons on Earth is caused by Earth's revolution and the tilt of its axis. As Earth revolves around the sun, its axis points the same direction all year. Therefore, when Earth is on one side of the sun, the bottom half of Earth is angled more towards the sun than the Northern Hemisphere. That means the sun's rays hit the Northern Hemisphere at more of an angle and it causes winter. However, on the other side of the sun the Northern Hemisphere is tilted towards the sun while the Southern Hemisphere is pointed away, causing winter in the bottom half of Earth. In March and September, neither hemisphere is tilted towards or away from the sun, so it is spring or fall.

Section 2 - Gravity and MotionWhat determines the strength of the force of gravity between two objects?

The strength of the force of gravity between two objects is determined by the masses of the objects and the distance between them. The greater the mass, the greater the object's gravitational pull. The greater the distance, the worse the object's gravitational pull and vice versa.

What two factors combine to keep the moon and Earth in orbit?

Inertia and gravity combine to keep Earth and the moon in orbit. Earth's gravity keeps the moon from straying out of its orbit, and inertia keeps the moon traveling around Earth without crashing into it. Same goes for the relationship of Earth orbiting the sun.

Section 3 - Phases, Eclipses, and TidesWhat causes the phases of the moon?

The phases of the moon are caused by changes in the relative positions of the moon, Earth, and the sun. As the moon orbits, the sun always lights half of it. From Earth, we can only see the half that we are facing, so when the moon is between Earth and the sun, we only see the part of the moon unlit by the sun. When the moon is behind Earth, it is only possible to see the lit side of the moon.

What are solar and lunar eclipses?

Solar and lunar eclipses happen when the moon's shadow hits Earth or Earth's shadow hits the moon. A solar eclipse happens when the moon travels directly in front of the sun, blocking sunlight from reaching Earth and blocking the view of the sun. A lunar eclipse happens when Earth is directly between the moon and the sun and Earth blocks sunlight from reaching the moon.

What causes the tides?

The tides are caused by differences in how much the moon's gravity pulls on different parts of Earth. The force of gravity pulls Earth and the moon towards each other, but the moon's gravitational pull isn't enough to pull the entire earth towards it to cause an orbit, but it is strong enough to yank the tides towards it. It causes high tides on the side of Earth closest to the moon and on the opposite side, because it is pulling Earth towards it, leaving water behind. Low tides happen between the two high tides.

Section 4 - Earth's MoonWhat features are found on the moon's surface?

Maria, craters, and highlands are the main features found on the moon's surface. Maria are dark, flat areas made of hardened rock formed from huge lava flows. Craters are large round pits, sometimes hundreds of kilometers across, caused by impacts of meteoroids. Highlands are mountains that cast dark shadows. They cover much of the moon's surface.

What are some characteristics of the moon?

The moon is dry and airless. Compared to Earth, the moon is small and has large variations in its surface temperature. Its diameter is a little less than the distance across the United States, about a quarter of Earth's diameter. It only has an eighth of Earth's mass. Temperatures have a much larger range, of -180°C to 130°C. They vary because it has no atmosphere, and gases can easily escape into space. The moon also has no liquid water, but there is evidence of possible patches of ice that remain frozen.

How did the moon form?

Scientists theorize that a planet-sized object collided with Earth to form the moon. Some of the rocky debris in the solar system, some the size of small planets, possibly could have been the object that may have collided with Earth. If so, material from the debris and Earth's outer layers was ejected into orbit around Earth, where it formed a ring. Gravity eventually caused the materials to combine and form the moon.